Astronomy Practice Exam

Which of the following statements about momentum is true?

1. Momentum cannot change in isolated systems.

2. Momentum can only be transferred, not conserved.

3. Momentum is created when forces are applied.

4. Momentum decreases with increased mass.

The correct answer is: Momentum cannot change in isolated systems.

Momentum is a fundamental concept in physics that describes the quantity of motion an object possesses. In the context of isolated systems, which are systems that do not exchange energy or matter with their surroundings, the principle of conservation of momentum states that the total momentum of such a system remains constant when no external forces act upon it. This is because momentum, defined as the product of mass and velocity, can be transferred between objects in a collision or interaction; however, the total momentum before and after the interaction remains unchanged when considered collectively within an isolated system. Therefore, the statement that momentum cannot change in isolated systems highlights this fundamental principle of conservation. The momentum may appear to change for individual objects involved in interactions, but the sum of their momenta remains constant in the absence of external forces. The other statements describe misconceptions or incorrect interpretations of momentum. For instance, momentum can be conserved and is not solely dependent on applied forces, which can influence its state but do not create the momentum itself; momentum already exists due to the mass and velocity of objects. Lastly, the idea that momentum decreases with increased mass is misleading, as momentum is directly proportional to mass—if mass increases while velocity remains constant, momentum will actually increase.